hello.c

The hello program displays a message on the screen
using the
printf
function, then exits. printf is defined in the
stdio.h library of input/output functions. That is why
we use #include directive.

Note the structure of the program: include directives,
followed by the definition of the function main.
The body of the function --- the working part of the
definition --- is the part enclosed in curly braces. Note
also the comments: the text enclosed /* like this
*/. Comments are meant to enlighten the human reader; the
compiler ignores them.